Non-foamed polyurethane sander pad for abrasive discs



1, 1957 E. w. PRATT ETAL 7 NON-FOAMED POLYURETHANE SANDER PAD FOR ABRASIVFJ DISCS Filed April 29, 1966 NVENTORS ERIC 'w. PRATT HAROLD A. HICKEY ATTORNEY United States Patent 3,333,371 NON-FOAMED POLYURETHANE SANDER PAD FOR ABRASIVE DISCS Eric W. Pratt, Lewiston, N.Y., and Harold A. Hickey,

Brookfield, Wis., assignors to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware Filed Apr. 29, 1966, Ser. No. 562,013 3 Claims. (Cl. 51-358) ABSTRACT OF THE DISCLOSURE A sander disc having a resilient non-foamed polyurethane pad molded about a central hub for mounting on a rotatable power-driven shaft. A disc of abrasive material is attached to the working face of the pad. The nonfoamed polyurethane pad has a hardness of from about 70 Shore A to 90 Shore A.

This application is a continuation-in-part of application Ser. No. 150,721 filed Nov. 8, 1961 and now abandoned.

This invention relates to a pad commonly called a sander pad which mounts a flexible sheet or disc of abrasive material, generally coated abrasive particles which are used for grinding, sanding, smoothing, bufling, and/or polishing a surface of a workpiece. The pad is adapted for attachment to a rotatively power-driven shaft and has sufficient flexibility to conform to curved surfaces but not so much flexibility that it bounces when engaging the surface to be ground, etc. Also, these pads have adequate strength to withstand centrifugal and torsional stresses encountered in high speed operation.

Examples of workpieces whose surfaces are ground, smoothed, sanded, buffed and polished by coated abrasive sheets are panels, sheets, plates, and strips of metal, wood and other material. Additionally, ridges formed by a welding operation and irregular surfaces on castings, etc. are removed by use of these sheets of coated abrasives mounted upon the rotatively-driven sander pads.

Heretofore, pads made from sisal and rubber performed satisfactorily but had a short life when subjected to severe working conditions such as continuous sanding of steel sheets. Under the severe working conditions, the disc of abrasive material becomes worn and/or torn whereupon abrasive wear occurs on the pad between the abraded rear side of the sheet and the front face of the pad to which the sheet is attached.

Our invention provides a sander pad which has outstanding resistance to abrasive wear and which has the required amount of flexibility to achieve fast and eflicient grinding, sanding, smoothing, buffing and polishing of curved surfaces. Specifically, our invention comprises a pad for operatively mounting a sheet of abrasive material for performing an operation upon a surface of a workpiece. The pad is adapted for use upon a rotatively driven shaft and comprises a hub member for effecting attachment of the pad to the shaft and preferably includes a reinforcing member.

A disc with a front face to which the sheet is mounted is molded around the hub and the reinforcing member so that it is disposed substantially transversely of the axis of rotation of the pad. This disc has a substantial thickness and it is made from a nonfoamed elastomer comprising essentially a urethane prepolymer and a cross-linking agent.

In the accompanying drawings, we have shown a preferred embodiment of our invention in which:

FIGURE 1 is a front elevation view of a sander pad incorporating our invention;

FIGURE 2 is a section view along the line IIII of FIGURE 1; and

3,333,371 Patented Aug. 1, 1967 FIGURE 3 is a front elevation view of a reinforcing member embedded within the pad and mounted upon a hub of the pad.

Referring to FIGURES 1-3 inclusive, we show a sander pad 1 comprising a metal hub 2 with a threaded bore 3 extending axially therethrough. This hub is adapted for engagement with a threaded end ofa :rotatively powerdriven shaft (not shown) for operatively mounting the sander pad thereon. The hub 2 has an annular shoulder 4 at one end which fits into an axial hole 5 of a metal reinforcing plate 6 substantially circular in shape with spaced apart radial projections 7 disposed in the plane of the plate. This reinforcing plate is joined to the hub at its annular shoulder 4 by welds 8 and 9 and located at substantially right angles to the central axis thereof.

Molded around the hub 2 and the reinforcing plate 6 is a disc 10 also disposed substantially perpendicular to the central axis of the hub with a central bore 11 coaxial with the bore 3 of the hub and the hole 5 of the reinforcing plate 6. FIGURE 2 shows the reinforcing plate embedded within the disc and the disc with a front side 12 and a front face 13 which engages the rear side of a sheet of coated abrasive particles (not shown). A well 14 at the central part of the face 13 leads inwardly towards the bore 11 to form a receptacle which receives the head of a short threaded bolt for attachment of the sheet of abrasives onto the face of the pad.

As shown, the disc has a substantial thickness and its rear side 15 is substantially frusto-conical. in shape. A- part 16 of the hub projects axially from the rear side of the disc and it is this part of the hub which engages the threaded end of the power-driven shaft.

The disc is made from a nonfoamed polyurethane elastomer which imparts outstanding abrasive resistance and a desired amount of flexibility to the pad. We have found that our pad enjoys good results in service when the polyurethane elastomer has a hardness of about 65 Shore A to about Shore D. Such an elastomer comprises a urethane prepolymer and a cross-linking agent which enters into polymerization with the urethane prepolymer. Urethane prepolymers which we have found satisfactory are made from polybutyletherglyooldiisocyanate. One such urethane prepolymer used in this invention is available from the du Pont Company, Wilmington, Delaware and is sold under the name Adiprene L-lOO. v

Some cross-linking agents which are useful include glycols, amines and diamines and particularly 4,4- methylene-bis-2,2 chloroaniline.

Preferred amounts of the aforementioned ingredients of the polyurethane elastomers include urethane prepolymer in amounts from about 60 to about parts by weight and a cross-linking agent in amounts from about 11 parts to about 28 parts by weight.

Production of the pad of FIGURES 1-3 uses apparatus having a barrel-shaped mold with an integral base plate and a male plunger with a port extending therethrough to permit excess elastomer fluid to escape from the mold. The mold has a contour corresponding: to the desired shape of the pad. Extending through the base plate is a hole through which is located a threaded centering stud. The hub of the pad with the reinforcing plate welded thereto is screwed onto the stud where it extends up through the base plate within the mold. Next, an elastomer liquid made from a urethane prepolymer and a crosslinking agent is poured into the mold to immerse the hub and the reinforcing plate. Then, the male plunger is placed in the mold and forced down until it engages a ledge stop during which time any excess elastomer liquid escapes from the mold through the port. To minimize air entrapment, the mold may be connected to a source of vacuum during filling thereof with the elastomer liquid.

Thereafter, the mold'with the elastomer liquid therein is cured at a desired'temperature for a given length of time. However, the pad may be removed after it has solidified sufliciently to retain its shape and then cured in an oven.

Extraction of the pad from the mold occurs after removal of the stud and lifting of the male plunger for freeing the pad therefrom.

The following examples illustrate methods by which abrasion resistant sander discs may be made according to this invention.

Example 1 An elastomer mixture containing 100 parts by weight of Adiprene L100 urethane prepolymer and 11 parts by weight of 4,4'-methylene-bis 2,2'-chloroaniline, a crosslinking agent, is added to a mold of the type described herein until the mold is full. Then, the plunger is operated as explained and the mold'with the elastomer mixture therein is cured at a temperature of about 158 F. for about 4 hours. The resulting pad has a hardness of about 90 Shore A.

Example 2 The same procedure as described regarding Example 1 is followed except that the mold containing the elastomer mixture is cured at about 250 F. for about 30 minutes. Pads made by the procedure of this example have a hardness of about 70 Shore A.

It should be noted that curing times and temperatures may be varied to alter the properties of sander discs made according to this invention. For example, raising the curing temperature and shortening the curing time, as shown in Example 2, tends to produce softer discs while increasing the curing time tends to produce harder sander discs. However, a preferred curing cycle used in forming sander discs having a hardness of 90 Shore A is shown in Example 1.

Various additives may be incorporated in the raw mix to effect the finished product in a desired way. For example, epoxy resins and pigments may be incorporated in the mix. It is preferred that the epoxy resin used in the raw mix have an epoxide equivalent between about 175 and 195. Epoxide equivalent as used herein is the grams of resin containing 1 gram equivalent of epoxide.

Our invention in sander pads effects outstanding and unexpectedly surprising advantages from the standpoint of service life. For example, field tests show our sander pad in service under severe conditions has a life of about eight weeks compared to a life of about three weeks for a sisal pad subjected to the same service conditions. Additional field tests demonstrate that our pad outlasts a conventional rubber pad 4 to 5 times,

Of significant importance is the fact that not only does our pad have the high resistance to abrasive wear but also a desired amount of flexibility.

While the resin shown in the examples is a specific polyether other ethers or esters may be used provided they produce a product as described in the claims.

While we have shown and described a preferred embodiment of our invention, it may be otherwise embodied within the scope of the following claims.

We claim:

1. A unitary, abrasion-resistant sander pad adapted for use on a rotatively driven shaft, said sander pad consisting essentially of a solid disc molded around a central hub member thereby providing a unitary pad, said disc being of substantial thickness and having a front face adapted for mounting a sheet of abrasive material, and a rear face, said disc being disposed substantially transversely of the axis of rotation of said pad and being formed from a nonfoamed polyurethane elastomer having a hardness of about 70 to about 90 on the Shore A scale thereby providing a disc having the combined characteristics of flexibility and resistance to abrasion, said non-foamed polyurethane elastomer consisting essentially of a urethane prepolymer and a cross-linking agent, said hub member projecting axially from the rear face of said disc for effecting attachment of said pad to said shaft.

2. A sander pad as defined in claim 1 wherein said non-foamed polyurethane elastomer is formed essentially of from about to about 100 parts by weight of a polyisocyanate prepolymer and from about 11 to about 28 parts by weight of a cross-linking agent selected from the group consisting of a glycol, an amine and a diarnine.

3. A sander pad as defined in claim 1 wherein said non-foamed polyurethane elastomer is formed essentially from about 100 parts by weight of polybutyletherglycoldiisocyanate and about 11 parts of 4,4-methylene-bis-2,2' chloroaniline, said non-foamed elastomer having a hardness of from about to about on the Shore A scale.

References Cited UNITED STATES PATENTS 2,581,567 1/1952 Wiley 5l--299 2,917,485 12/1959 Gladding et al. 26077.5 2,950,584 8/1960 Welch 51298 3,036,996 5/1962 Kogon 260--77.5 3,252,775 5/1966 Guilbert 51-298 ALEXANDER H. BRODMERKEL, Primary Examiner.

DONALD J. ARNOLD, Examiner. 

1. A UNITARY, ABRASION-RESISTANT SANDER PAD ADAPTED FOR USE ON A ROTATIVELY DRIVEN SHAFT, SAID SANDER PAD CONSISTING ESSENTIALLY OF A SOLID DISC MOLDED AROUND A CENTRAL HUB MEMBER THEREBY PROVIDING A UNITARY PAD, SAID DISC BEING OF SUBSTANTIAL THICKNESS AND HAVING A FRONT FACE ADAPTED FOR MOUNTING S HEEET OF ABRASIVE MATERIAL, AND A REAR FACE, SAID DISC BEING DISPOSED SUBSTANTIALLY TRANSVERSELY OF THE AXIS OF ROTATION OF SAID PAD AND BEING FORMED FROM A NONFOAMED POLYURETHANE ELASTOMER HAVING A HARDNESS OF ABOUT 70 TO ABOUT 90 ON THE SHORE A SCALE THEREBY PROVIDING A DISC HAVING THE COMBINED CHARACTERISTICS OF FLEXIBILITY AND RESISTANCE TO ABRASION, SAID NON-FOAMED POLYURETHANE ELASTOMER CONSISTING ESSENTIALLY OF A URETHANE PREPOLYMER AND A CROSS-LINKING AGENT, SAID HUB MEMBER PROJECTING AXIALLY FROM THE REAR FACE OF SAID DISC FOR EFFECTING ATTACHMENT OF SAID PAD TO SAID SHAFT. 